Simulations and reconstruction of antiproton-matter annihilation events in antimatter experiments

Il modello standard (SM) è ad oggi la teoria più completa che siamo riusciti a formulare per descrivere i componenti fondamentali del nostro universo e le loro interazioni. Con essa è possibile descrivere con grande precisione un'incredibile quantità di fenomeni. È ben noto, tuttavia, che il modello standard non è né completo né pienamente compreso. Un esempio importante è l'incapacità di spiegare con il SM l'asimmetria osservata su scala cosmologica tra la presenza di materia e antimateria. Uno delle strade seguite a livello sperimentale per affrontare questo argomento è quella di verificare delle possibili violazioni della simmetria di CPT. I progetti presentati in questa tesi sono inquadrati all'interno di un esperimento che indaga questa particolare tematica. ASACUSA è un esperimento che si svolge al CERN e che mira a indagare diversi aspetti dei sistemi di antimateria. La collaborazione porta avanti diversi progetti in parallelo. Il principale si focalizza su un test di CPT che si basa sulla misura di spettroscopia iperfine dell'anti-idrogeno per confrontare la sua struttura iperfine con quella ben conosciuta dell'idrogeno. Un linea di ricerca di ASACUSA con finalità più pratiche è quella che mira invece a caratterizzare i prodotti delle annichilazioni di antiprotoni a riposo. Lavorando in ASACUSA ho contribuito negli anni sia alla messa a punto e all'aggiornamento della parte hardware sia a vari progetti di analisi e simulazione dei dati. In questa tesi presenterò due contributi a queste due linee di ricerca. Il primo riguarda lo sviluppo di simulazioni Monte Carlo (MC) per lo studio dei prodotti dell'annichilazione di antiprotoni su diversi materiali e inoltre la digitalizzazione di queste e altre simulazioni di questa misura. Oltre a collezionare dati di annichilazione di antiprotoni a riposo, l'obiettivo di questa ricerca è quello di testare i software MC confrontando le simulazioni con i dati sperimentali. Questi processi sono essenziali per la maggior parte delle misure nel campo dell'antimateria a bassa energia e i modelli su cui si basa il software di simulazione MC si basano su estrapolazioni dai dati per riprodurre questi processi a basse energie. Il secondo contributo è l'implementazione del software di ricostruzione del segnale per il rivelatore a barre scintillanti usato per la calibrazione della fase di creazione dell'anti-idrogeno. Questo rivelatore chiamato DANTE (Detector for ANnhilation of Tracking Experiments), nell'ultimo anno è stato sottoposto a un aggiornamento completo, sia hardware che software, per l'utilizzo nel prossimo periodo di acquisizione dei dati. Uno di questi upgrade è stata l’implementazione di un software di ricostruzione delle tracce delle particelle. Questo contributo è di fondamentale importanza per il processo di misurazione della spettroscopia dell'anti-idrogeno. Il rivelatore DANTE viene attualmente utilizzato per tracciare i pioni e altri prodotti di annichilazione nell'area di mixing di positroni e antiprotoni dell'esperimento. Ciò consente di monitorare il plasma di antiprotoni in questa fase delicata. La tesi si sviluppa come segue: nel primo capitolo si introducono alcuni concetti relativi al campo di ricerca sull'antimateria e alcuni tratti generali che caratterizzano la ricerca sperimentale in fisica delle particelle. Nel secondo capitolo descrivo l'apparato sperimentale di ASACUSA. Nel terzo capitolo mi concentro sulla descrizione dei due progetti di ricerca svolti in ASACUSA dove si inquadra il mio contributo all'esperimento. Dedico poi gli ultimi due capitoli ai due progetti sviluppati in questo lavoro di tesi. Concludo quindi con un riassunto dei risultati e menzionando alcuni possibili sviluppi di questi progetti. Del materiale aggiuntivo è riportato nelle due appendici dedicati ai due progetti.The Standard Model (SM) is to date the most comprehensive theory describing the fundamental components of our Universe and their interactions. With it, an incredible amount of phenomena can be described with great precision. It is well known, however, that the standard model is neither complete nor fully understood. An important case of SM incompleteness is the inability to explain the observed asymmetry between antimatter and matter on a cosmological scale. One way pursued experimentally to address this issue is to test for possible CPT symmetry violations. The projects I am presenting in this thesis are framed inside an experiment that deals with this particular research subject. The Antimatter Spectroscopy And Coherent Upward-going Scattering experiment (ASACUSA) is held at CERN and it aims to investigate several aspects of antimatter systems. Its collaboration carries on several projects. The main one focuses on a CPT test which uses hyperfine antihydrogen spectroscopy measurements, in order to compare the hyperfine structure of antihydrogen with the well known one of hydrogen. Another line of research that started in the last years, aims at characterize the products of antiproton annihilation at rest. In this collaboration I have contributed over the years both to the set-up and upgrade of the hardware part and to various data analysis and simulation projects. In this thesis I will present two main contributions carried out within the framework of these two lines of research. The first concerns the development of Monte Carlo (MC) simulations for the study of slow anti-proton annihilation products on different materials and then the digitization of these and other simulations of this measure. Other then collect data about annihilations at rest the goal of this research is to compare MC software output with experimental data, since they are not quite reliable for this process. The annihilation processes are essential for most measurements in the field of low-energy antimatter and, in addition, the models on which MC simulation software is based rely on extrapolations from data to reproduce these processes at low energies. The second focus on the implementation of a signal reconstruction software for the scintillating bar detector used for the calibration of the creation phase of antihydrogen. This detector, called DANTE (Detector for Annihilation Tracking Experiment), has undergone a complete upgrade in the last year, both hardware and software for use in the next data taking period. One of these upgrades was the implementation of a tracking reconstruction software. This contribution is of fundamental importance for the process of making the anti-hydrogen spectroscopy measurement. The DANTE detector is currently being used to track pions and other annihilation products in the positron and antiproton mixing area of the experiment. The software makes it possible to monitor the cloud of antiprotons at this delicate stage. The thesis is developed as follows. In the first chapter, I introduce the research of antimatter at low energy and some general traits that characterize experimental research in particle physics. In the second chapter I will describe the experimental apparatus of ASACUSA. In the third chapter, I will focus on the two lines of research carried out in ASACUSA, where our contribution is framed. I will then devote the last two chapters to the two projects developed in this thesis. I will conclude with a summary of the results and mentioning some further possible developments of these projects. Some additional material about the projects can be found in the appendixes

Cumulative and Ratio Time Evaluations in Keystroke Dynamics To Improve the Password Security Mechanism

The password mechanism is widely adopted as a control security system to legitimate access to a database or a transaction content or computing resources. This is because of the low cost of the mechanism, the software routine simplicity, and the facility for the user. But the password mechanism can suffer from serious vulnerabilities, which have to be reduced in some way. An aid comes from the keystroke dynamic evaluation, which uses the rhythm in which an individual types characters on a keyboard. It has been demonstrated how the keystroke dynamics are unique biometric template of the users typing pattern. So, the dwell time (the time a key pressed) and the flight time (the time between “key up” and the next “key down”) are used to verify the real user’s identity. In this work we investigated the keystroke dynamic already reported in literature but with some differences, so to obtain additional benefits. Rather than the commonly adopted absolute times (dwell and fly times), we deal with cumulative and ratio ones (i.e. sum and ratio of dwell and fly times), taking into account that the latest are times which do not change even if the user’s typing style evolves with practic

Features of the Primordial Universe in f(R)-gravity as viewed in the Jordan frame

We analyze some relevant features of the primordial Universe as viewed in the Jordan frame formulation of the f(R)-gravity, especially when the potential term of the non-minimally coupled scalar field is negligible. We start formulating the Hamiltonian picture in the Jordan frame, using the 3-metric determinant as a basic variable and we outline that its conjugated momentum appears linearly only in the scalar constraint. Then, we construct the basic formalism to characterize the dynamics of a generic inhomogeneous cosmological model and specialize it in order to describe behaviors of the Bianchi Universes, both on a classical and a quantum regime. As a fundamental issue, we demonstrate that, when the potential term of the additional scalar mode is negligible near enough to the initial singularity, the Bianchi IX cosmology is no longer affected by the chaotic behavior, typical in vacuum of the standard Einsteinian dynamics. In fact, the presence of stable Kasner stability region and its actractive character are properly characterized. Finally, we investigate the canonical quantization of the Bianchi I model, using as time variable the non-minimally coupled scalar field and showing that the existence of a conserved current is outlined for the corresponding Wheeler-DeWitt equation. The behavior of a localized wave-packet for the isotropic Universe is also evolved, demonstrating that the singularity is still present in this revised quantum dynamics.Comment: 20 pages, 8 figure

Green Polymers in Personal Care Products: Rheological Properties of Tamarind Seed Polysaccharide

Tamarind seed polysaccharide (TSP) is a xyloglucan of vegetable origin, recently proposed for the cosmetic and pharmaceutical market as a "green" alternative to hyaluronic acid. In this study, TSP water dispersions, at different concentrations, were characterized by means of rheological measurements, both in continuous and oscillatory flow conditions. The results were compared with those of hyaluronic acid of two different molecular weights. The results pointed out the close rheological behaviors between TSP and hyaluronic acid with comparable molecular weight. Afterwards, the structural features of binary and ternary polysaccharide associations prepared with TSP, hyaluronic acid (very high MW) and dehydropolysaccharide gum, a modified xanthan gum, with high stabilizing properties, were investigated. The rheological properties were significantly affected by the polysaccharide ratios in the mixture, suggesting that the combination of TSP with other polymers can lead to a modulation of the texture and functional properties of cosmetics

Combining high-resolution scanning tunnelling microscopy and first-principles simulations to identify halogen bonding

Scanning tunnelling microscopy (STM) is commonly used to identify on-surface molecular self-assembled structures. However, its limited ability to reveal only the overall shape of molecules and their relative positions is not always enough to fully solve a supramolecular structure. Here, we analyse the assembly of a brominated polycyclic aromatic molecule on Au(111) and demonstrate that standard STM measurements cannot conclusively establish the nature of the intermolecular interactions. By performing high-resolution STM with a CO-functionalised tip, we clearly identify the location of rings and halogen atoms, determining that halogen bonding governs the assemblies. This is supported by density functional theory calculations that predict a stronger interaction energy for halogen rather than hydrogen bonding and by an electron density topology analysis that identifies characteristic features of halogen bonding. A similar approach should be able to solve many complex 2D supramolecular structures, and we predict its increasing use in molecular nanoscience at surfaces

The inelastic hard dimer gas: a non-spherical model for granular matter

We study a two-dimensional gas of inelastic smooth hard dimers. Since the collisions between dimers are dissipative, being characterized by a coefficient of restitution $\alpha<1$, and no external driving force is present, the energy of the system decreases in time and no stationary state is achieved. However, the resulting non equilibrium state of the system displays several interesting properties in close analogy with systems of inelastic hard spheres, whose relaxational dynamics has been thoroughly explored. We generalise to inelastic systems a recently method introduced [G.Ciccotti and G.Kalibaeva, J. Stat. Phys. {\bf 115}, 701 (2004)] to study the dynamics of rigid elastic bodies made up of different spheres hold together by rigid bonds. Each dimer consists of two hard disks of diameter $d$, whose centers are separated by a fixed distance $a$. By describing the rigid bonds by means of holonomic constraints and deriving the appropriate collision rules between dimers, we reduce the dynamics to a set of equations which can be solved by means of event driven simulation. After deriving the algorithm we study the decay of the total kinetic energy, and of the ratio between the rotational and the translational kinetic energy of inelastic dimers. We show numerically that the celebrated Haff's homogeneous cooling law $t^{-2}$, describing how the kinetic energy of an inelastic hard sphere system with constant coefficient of restitution decreases in time, holds even in the case of these non spherical particles. We fully characterize this homogeneous decay process in terms of appropriate decay constants and confirm numerically the scaling behavior of the velocity distributions.Comment: 21 pages, 6 figures and 2 tables, submitted to JC